1. Field of the Invention
The present invention relates to the growth of non-polar m-plane III-nitride film using metalorganic chemical vapor deposition (MOCVD).
2. Description of the Related Art
Gallium nitride (GaN) and its ternary and quaternary compounds are prime candidates for fabrication of visible and ultraviolet high-power and high-performance optoelectronic devices and electronic devices. These devices are typically grown epitaxially by growth techniques including molecular beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD), or hydride vapor phase epitaxy (HVPE).
The selection of substrate is critical for achieving the desired GaN growth orientation. Some of the most widely used substrates for III-N growth include SiC, Al2O3, and LiAlO2. Various crystallographic orientations of these substrates are commercially available.
FIGS. 1(a) and 1(b) are schematics of crystallographic directions and planes of interest in hexagonal GaN. Specifically, these schematics show the different crystallographic growth directions and also the planes of interest in the hexagonal wurtzite GaN structure, wherein FIG. 1(a) shows the crystallographic directions a1, a2, a3, c, <10-10> and <11-20>, and FIG. 1(b) shows planes a (11-20), m (10-10) and r (10-12). The fill patterns of FIG. 1(b) are intended to illustrate the planes of interest, but do not represent the materials of the structure.
It is relatively easy to grow planar c-plane GaN due to its large growth stability window. Therefore, nearly all GaN-based devices are grown parallel to the polar c-axis. However, as a result of c-plane growth, each material layer suffers from separation of electrons and holes to opposite faces of the layers. Furthermore, strain at the interfaces between adjacent layers gives rise to piezoelectric polarization, causing further charge separation.
FIGS. 2(a) and 2(b), which are schematics of band bending and electron hole separation as a result of polarization, show this effect, wherein FIG. 2(a) is a graph of energy (eV) vs. depth (nm) and represents a c-plane quantum well, while FIG. 2(b) is a graph of energy (eV) vs. depth (nm) and represents a non-polar quantum well.
Such polarization effects decrease the likelihood of electrons and holes recombining, causing the final device to perform poorly. One possible approach for eliminating piezoelectric polarization effects in GaN optoelectronic devices is to grow the devices on non-polar planes of the crystal such as a-{11-20} and m-{1-100} planes family of GaN. Such planes contain equal numbers of Ga and N atoms and are charge-neutral.
Planar {1-100} m-plane GaN growth has been developed by HVPE and MBE methods. However, prior to the invention described herein, planar m-plane GaN growth had not been accomplished with MOCVD.